Background: In 2008, it was estimated that 2.3% (1.08 million) of Thai adults had ever used kratom. Generally, kratom-related problems are ignored. While polysubstance use is common, little has been known about this issue in kratom users. We aimed to explore the lifetime history of substances use among Thai kratom users.

Methods: The national household survey on prevalence of substance use among Thai adults was conducted in 2011. A multistage random sampling technique was used. Each selected member was interviewed using structure questionnaire. The risks of other substance uses were compared between respondents with and without a history of kratom use.

Results: Of the total sample (18,457), 544 (2.9%) had ever used kratom. Common route of administration was chewing fresh leaves. Their mean age (SD) was 42.7 (12.8) years old, 459 (84.4%) were male and 264 (48.5%) used other illicit drugs at least once in their lifetime. The use of other illicit drugs were higher than those of alcohol and tobacco. They were significantly more likely to use heroin [adjusted odds ratio (AOR) =39.7; 95% confidence interval (CI) =20.9-75.5], ecstasy and ice [AOR (95%CI) = 30.5 (15.2-61.1) and 29.1 (16.2-52.2) respectively].

Conclusions: Comparison with those who have never used kratom, those with a lifetime history of kratom use have much higher risks of other substance uses, especially the uses of heroin, ecstacy and ice. Although kratom-related disorders are still on debate, the high risks of other substance uses suggest a need for health assessment among kratom users.